1. Field of the Invention
The present invention relates to a recording apparatus applicable to office or telecommunication equipment such as a copying machine, a facsimile terminal equipment, a word processor, office computer and the like. And more particularly, the present invention relates to an ink jet recording apparatus and method for detecting recording liquid wherein the recording is performed by discharging the ink to form ink droplets, which are made to stick onto a recording medium such as a paper.
2. Related Background Art
Recently, the ink jet recording apparatus has been used much more due to the advantages of excellent print quality, recording speed, quietness during operation, and easiness of coloring.
An ink jet recording head (thereafter referred to as head) equipped in such a recording apparatus is largely classified into two types, depending on the preservation state of ink.
The first type is one in which the replacement is not presumed as a rule (thereafter referred to as a permanent type) as a storage container of ink is provided outside of a head body to supply the ink within the storage container to the head by means of a supply tube. With this type of head, if the ink has been exhausted, the recording can be resumed by refilling the ink into the storage container, or exchanging each storage container. It should be noted that a type being able to replace only a recording head or storage container independently is contained in this type. The second type is one in which a storage container of ink is provided integrally with a head body (thereafter referred to as disposable type), and at the time when the ink within the storage container is used up, the entire head and storage container are replaced.
By the way, with such an ink jet recording apparatus, if a little ink remains, or dries within a liquid channel or dries and fixes on a portion of discharge ports for discharging liquid because it is not used for a long time, the recording may not be often carried out without blurred recorded characters.
In a recording head provided with the elements such as electricity-heat converters generating the heat energy which is used for discharging ink, a so-called idle heating state occurs when the ink does not exist in the vicinity of heat energy generating elements, so that there is a high possibility that electricity-heat converters or component members of liquid channels are damaged, as well as a failure in recording. More specifically, an example of a recording apparatus with a head in such a method is a recording apparatus which is provided with electricity-heat converters within a liquid channel of ink in the vicinity of ink discharge ports, causing the film boiling in the ink with the heat energy which the electricity-heat converters generate, and discharges the ink with the growth of bubbles due to the film boiling.
The above-mentioned problem must be of course avoided in the permanent type, while it is also taken into consideration to avoid unnecessary replacement of recording head or abrupt stop of recording in the disposable type.
Conventionally, in the permanent type, a method has been proposed for detecting whether a little ink remains, based on a reduced amount of ink pressure, with a pressure sensor provided within the storage container or ink. While in the disposable type, another method has been proposed for detecting whether a little ink remains, based on changes of the electric conductivity of ink within the storage container of ink.
However, there are following problems for detecting remaining ink with those methods.
First, with a recording head for use in a serial recording apparatus where the recording is conducted by moving the head back and forth in a reciprocatory motion along a recording medium (recording paper), the ink undergoes changes along with the movement of the head engaged, causing a fluctuation of the liquid surface to be measured, so that a detected amount of ink pressure or electric conductivity is varied to bring about a malfunction in detecting remaining ink.
Second, with the above-mentioned method, it is difficult to detect immediately before the ink is exhausted completely, as no ink is detected in a condition where the ink still remains, so that the ink can not be used until its full amount, leaving some waste. Further, owing to the ink leaking from a discarded storage container of ink, the surroundings may be stained.
Thus, a recording apparatus and method for detecting ink is desired wherein it is provided with the feature for reliably detecting immediately before the ink is exhausted completely, so as to be able to use the ink until its full amount.
On the other hand, U.S. Pat. No. 4,550,327 discloses a liquid droplet discharge apparatus in which the liquid within a nozzle is discharged by use of the heat energy, and in which a plurality of nozzles each comprises a conductor section in the inside thereof, and the state of liquid within each nozzle is sensed by detecting changes of current value flowing through the conductor section.
However, there are some occasions where as the conductor section is provided within each nozzle and abuts on a heat energy generating element for discharging liquid, the heat energy caused by the conductor section has an effect on the discharge of liquid. And as there is a necessity of providing the conductor section for each nozzle, the manufacturing process is complex, resulting in a higher manufacturing cost.
Further, as the conductor section exists within nozzle, the recording is stopped simultaneously with the sensing of no liquid within nozzles.